Permanent magnet electrodynamic transducer



w. E. GILMAN April 27, 1948.

- PERMANENT MAGNET ELECTRODYNAMIC TRANSDUCER Filed July 4, 1942 2 Sheets-Sheet 1 I d I Ufl/orrzeys April 27, 1948. -w. E. GILMAN PERMANENT MAGNET ELECTRODYNAMIC TRANSDUCER 2 Sheets-Sheet 2 Filed July 4, 1942 x r w Z a J am; w

Patenied Apr. 27, 1948 PERMANENT MAGNET ELEQTIRODYNAMIC TRANSDUCER -Webster E. Gilm'an, A Maywo'o'd', I lla, assignor -to, :Permoflux Corporation, Chicago, 111., a corporat tion of Illinoi's Application luly l, 1942, Serial No. 449,767

zblaims. (Cl. 1719--1i-15r5) This invention relates to'transducers and-particularly to the dynamic type as contrasted-with the magnetic type thereof.

Transducers of the dynamic. type may, of course, be employed 'either'as speakers or 'as microphones, andin either of these'usesfthefidelity and range of irequency response is in a large measure dependent upon the accuracy of :formation location and relationship-of thevarious-elementsrithereof, and is particularly-(lopendent:upon the accuracy of location-of the voicecoilstrmture in the magnetic :gap of "the vtransducer. While it has been possible, through the exercise of great care and skill, to obtain the-desiredzoperationalcharacteristics in prior dynamic transducers, the difficulties involved have often resultedin wide variations of construction andperformance, and to enable such difiiculties to he overcome in a simple and expeditious manner is an-rimportan object of thisinvention.

The aforesaid difiiculties of 1 producing the desired-performance characteristicsin, prior dynamic'transducers have, of-course, been encountered in transducers of vvarious sizes and designs, but where such transducers have "been-of 'a-relativelyrsmall size, the reduced tolerancesand theredueed size have further increased the diflicultles involved in producing a satisfactory dynamic transducer, and a further object of this invention is. to enable fidelity and wide frequency response to be readily and uniformly attained particularly in dynamic transducers -of relatively small size. Furtherobiects related-to the foregoing are to so form and arrange the elements of-themagnetic circuit in such transducers as to assure accuracy of size and location :of the magnetic gap; to simplify the-location and mounting of the diaphragm; to insure accurate location of the diaphragm relative to the magnetic gap; toeenable the voice coll-to be readily located --in an accurately determined position on the voice coil support; and to so form and interrelate the pole pieces of the magnetic circuit and the diaphragm and the voice coil structure that uniformity and accuracy of relationship are invarand by-reason of the number'cf :parts and numher .of accurate connection-s involved the cost of production has been relatively high. Moreover, in those instances where the proper degree of skill and caretlfias' notbeen exercised ih assembung- :the "numerous :parts, the "quality or :performance abeeh: relatively low in transducers of the rafcres'aid'echaracter; :lt ist therefore, another object of thissinvention toisimplity theip'roa duction oi the magnetic lcitcuitfof fdynamic transducers ahcl the ilikej and fturth'er object's related toxithe foregoing":are-Ito:rsoJ.-torm. and rlate "the elements oi the ma'gneticcircuitmfdyrfaniic transducers that accuracy of relation df thezelements thereof-ls :attained as an :ln'cidentrto (the assembly OfISU-Ch' elements; toienableiafpermanent magnet zu's'ed-r asralpart -of thezmagnetic'circuitrin such a itransducer "ito ifunctionisinirproducingi proper interrelation of the tether lparts'j .to reduce ithe number" ofzlparts employed; and the number 'of connecting operations "required in' the iprod uc tion fof =5 such wm'agzietic circuits; to :enable both polesolkalpermanenhmagnetzforiuseinsuch magnetic circu'its to he engaged in :a, magnetic sense witmtheinrespective .pble piecesdn 'al similar'mam ner to thereby simplify-the interconnection of the -engaged-;parts wand to iprovide a; permanent magnet *of novel and advantageous: form for use 525 in=the magnetlc circuits of suchdynamic transdu'cers. a

:In' the usefof transducers; whether they hea em= bodied as microphonesror:asf speakers, it isf'customary-tospr'ovide a'separately-zformed supportingmounting :member which not only acts "as a carrier tor the transducer but also serves "as a carrier tor "the =connectingvleads which are to be electrically associated with :the voice coil 1 of the transducer-j Ihe iaoili y'w t hi h "t a ducers;=1nay be associated with such a: carrieror mounting means iSf-Oftfifl an important "factor in the use-of equipment of; this character, and it is a further object of this invention to enable transducers to he solmounted upon "a headband or other support in a-simple -and elfective-mannerrand-a 'related object is to accomplish this end by means oftaisimple-and-noveleharacter. Other bje ts related-t0 the; toregoing are" to enable the desired electrical connections to the transducer to be established as an incident to the mounting of suchia transducer-ion asupport such as aheadbandland to enable aheadband iorr uchuseto be simplynandeconomically produced.

Other and further objects; of the :present invention will be apparent "from the :following -deseription and claims i' and are illustrated in the accompanying drawings which, by way-of illustration, showpreferred embodiments and the principle thereof and-what I' 'IlOW;';GQnSidI to be thei-bestmode in which Ihaverontemplated applying that principle. Other embodiments of the invention embodying the same or equivalent principle may be used and structural changes may be made as desired by those skilled in the art without departing from the present invention and the purview of the appended claims.

Inthe'drawings: I] n Fig. 1 is a perspective view illustrating the invention as embodied in a headset having relatively small dynamic speakers at opposite ends of the head band;

Fig. 2 is an elevational view of of one of the speakers;

Fig. 3 is a cross sectional view taken substantially along the line 3-3 of Fig.2;

Fig. 4 is a sectional view taken substantially along the line 4-4 of Fig. 3; V M

Fig. 5 is an enlarged fragmental view show: ing a part of the structure illustrated in Fig. .3;

Fig. 6 is a view similar to Fig. 3 and illustrating another embodiment of the invention;

Fig. 7 is a view similar to Fig. 2, and. illustrating still another embodiment of the invention;

Fig. 8 is a cross sectional view taken substantially along the line 8-8 of Fig. 7

Fig. 9 is an enlarged fragmental view showing part of the structure illustrated in Fig. 8;

Fig. 10 is a cross sectional view similar to Fig. 8 and illustrating a further embodiment of the invention; and

' Fig. 11 is an elevational view similar to Fig. '7 and showing another manner of mounting.

While the present invention relates to transducers and may be utilized in both microphones and speakers with equal facility, it is herein disclosed as particularly applied to speakers, and in the form shown in Figs. 1 to. 5 of the accompanying drawings, the invention'is embodied in a relatively small dynamic speaker f0 adapted for mounting on a head band I! or the like so that the speaker l0 may be held in close association with an ear of the user; The speaker I0 is'generally cylindrical in cross-section and has a housing l2 closed at its outer end by a mounting plate l3 made froman insulating'material such as a synthetic resinous product and through which the speaker is adapted to be mounted on the head band In accordance with the present invention the speaker 10 embodies a diaphragm l4 located within the housing [2 "relatively close to the outer or larger end thereof, and means for actuating and controlling the diaphragm M are disposed within'the' housing |2 between the diaphragm l4 and'the inner or output end of the speaker and are so formed that a loading passage or cavity extends therethrough'to efficiently transmit the sound created [by the diaphragm to "the passages of the ear of the user.

The magnetic circuit of the present speaker includes a permanent magnet |,5 having a central hub It with a central bore formed axially therethrough, and at one of its ends the hub l6 has an annular skirt 3 which projects radially therefrom and then extends errdwise to terminate in an annular face l9 which is'preferably located in the plane of the annular-end face 20 of the hub l6. Thus the annular face- I9 of the skirt and the annular face 20 of the hub l6 constitute the opposite poles of the permanent magnet l5. Concentric annular pole pieces 2| and 22 mad from soft iron or like material are disposed in abutment with theannular pole faces I9 and 20 of the permanet magnet, the inner pole piece 22 having a oentral bore or opening 23-formed therein in alignment with the bore I] of th'epermathe outer end nent magnet. A locating or centering ring 24 made from a non-magnetic material such as brass is disposed with its opposite edges seated with a press fit in annular rabbeted grooves 26 and 21 formed in the adjacent annular corners of the pole pieces 2| and 22, and hence the spacing ring 24 acts to locate the opposed annular faces of the pole pieces 2| and 2,2 in accurately spaced relation, thereby to define an annular magnetic gap 30 within which the voice coil structure 3| associated with the diaphragm I4 may operate.

The central pole piece 22 isheld in an accurately determined relation to the central hub It or the-magnet by a tubular eyelet 32 which extends with a relatively snug fit through the openings 23 and I"! in the pole piece 22 and the hub It. At one of its ends the eyelet 32 is outwardly flanged as at 34 into a socket 36 which is countersunk into the outer face of the pole piece 22 concentric with the axis of the bore 23, while at its other end the eyelet 32 is flanged outwardly at 38 to engage the end face 39 of the magnet |5. Since the spacing ring 24 has a press fit with respect to the two pole pieces 2| and 22, the eyelet 32 acts through the spacing ring 24 to hold the pole p-iece 2| firmly against the annular face IQ of the magnet, and if desired the spacing ring 24 may be made a slightly coned form and may be so disposed in the grooves 26 and 21 that the ring is drawn toward a'flat form as the eyelet 32 is flanged into place. merit a firm engagement of the outer pole piece 2| with the annular face l9 of the magnet I5 is V invariably assured.

The diaphragm [4 has its outer or bordering edge clamped between an annular border flange '40 on the mounting plate l3 and an opposed clamping face provided on the pole piece 2|, and this is accomplished by so forming the housing |2 that it exerts the requisite clamping action between the pole piece 2| and the mounting plate l3. Thus, as shown in Fig. 3 of the drawings, the housing lz has a cylindrical portion l2 which surrounds the pole piece 2| and the peripheral edge of the mounting plate [3, and the housing is offset inwardly to form an annular shoulder 4| facing endwise toward the outer end of the speaker l0 and engaging the face of the pole piece 2| which is remote from the diaphragm l4. The desired clamping action is obtained by spinning the end edge of the cylindrical portion l2 of the housing radially inwardly to form a flange 42 which overlies the face of the mounting plate l3 and holds the same in firm abutment with the pole piece 2|. Beyond the shoulder 4| toward the inner end of the speaker the housing I2 is formed so as to be rounded inwardly as' at 43 and this'rounded portion of the housing I2 terminates in an opening 44 which is substantially concentrio with the axis of the eyelet 32. The opening 44 in the housing is somewhat larger than the central opening of the tubular eyelet 32, and a protectin member 45 which is generally in the nature of a grommet is inserted into the opening 44 so that its central opening 46 forms a continuation-of the central opening of the eyelet 32. The inner flange 41 of the grommet 45 extends radially outwardly into the space between the surface 39 of the permanent magnet and the inner surface of the housing 2, while the outer portion of the grommet 45 extends for a considerable distance radially outwardly and about the rounded surface 43 of the housing l2. Thus the grommet 45, which is' preferably made from a resilient material such as rubber,'may be pressed Through such an arrangeamassiexternal auditory cana of thef-nser. Froin tliisfl tangerine-grommet 155185121; practice; shiedte fitainto the entranceto the external auditerycanal of -the a erage-adnit inal andthe othr parts of; the"speak-er;- areqrelated in size to this resilient 11 force upon the magnet- I 5 to; thereby cooperatewitwtheeyelet 3 2 and the press-fitconnection between the two pole pieces t insure firm contactof thepole face IS With theg annularpole piece 21.

The;vciee--coil'=structureflqcomprises a coil 01" wire th atis wound npon tlie out er surface of the cylindrical supporting form made from a rela tively stiit ma terial si-zcl'i as; impregnated I paper orthe'lik e-y and the voice coil structure 31 1 is so mounteel onthediaphragm I that the-voice coil structure-may exte itl from the diaphragm man an axial direction into the annularmagnetic'gap- 30: It isrecognized that fidelity andaccurate response throughout a -wide frequency range-arein a largemeasure-dependent upo'n': accurate location or Spacing of the voice coil strncture'in the annular magnetic gamandin raccoi dance= with-the-present "invention-the diaphragmfl 4, the voice coil-structure 3'1 "andthe I diaphragm supprting=means= are constructed and'frelated 'in anovelmanner which-insuresthe;desired accuracy of--re1 ation" and location for these elements with respect; to each" otherand-"with respect to the" magnetic-gap 3'0? To this end} thediaphragm- I 4'; whichris pre fer ablj} formed-from paper-impre'gnated with ma 4 terial such asasynthetic resiri of phenokaldehyde type; is molded or otlierwise formed ta ern body' laterialpositioning-"means adapted to cooperat with complementa-I' means on the voice coi1 structure -3 I to*-i'nterlo'ck the voice'eoil structura inaf predeterminedand preferasblyconcentric're lationship with-respectto the diaphragm; Iii-the embo dimentof the invention illiis'tratedin Figsii. 1' to I 5 of the drawings; this end is '-.attairied by= molding the=- diaphragm I t with'- *an- -ofiset cy1i n=- drical wall section 50 of such adiameter as to snug-ly withinthe cylindrical coil supporting form 49 and tliemoil suppcrting form dil is" secnred*-in position about the cylindrical wall-SI) by adhesive or ofther 1 suitable=means Radially outwardlyrof the cylindrical wall- 50 thediaphragm I 4=- is molded' or otherwise 1 formed 5 toizprovide a; readily: bendable"- and relati'vely flat annularaportion 51; which at itsouter edges is-merged with-an annualarzconnecting portion sz disposed-rat an angle to mafia; portiorr 51s Thea connectiugsporti0n-52" merges with: a: relatively short; or' narrow: cylindricalmwalli-section ic whichg i turn, .joins :with

an outwardly projecting edgecfiange-ibdisposed lationstosthezannulammagneticlgap 30;: andrithis;

endiais:iattainedzthroughsthaaprovistonanti aicbop 6: erating -annular shoulder 'formed on tlie polev piece 21 *so jas- -to mes: mar 1 1w ontwardlia and' adapted to fiti snuglywith cynnsriear eating wadl i fli ofi the lasm 5 55 isformed so asto e concentriawith the an nular magnetic ga amg while-the; cylin diical lo-- eating wall 53 is-so formed on -thediapiiragml as to' be concentric with-=the-annu1ar :cylindr-ical wall5'B-and the-Woice coil structure -3 I;- and hence 10 when=the-wall EB isfitted 'over-and about 'theteredfand th'evoi-ce =coil structure- 3 I} is} 'dli'sposed i111 the desired 'concentric relati onin the annular magnetic gap 30:- As --a'-furth"er aid ih- -prod i1cin a-ecurate and uniform assemblyof the speak thefi angeJO- Of the f OutQ1-Wa-11 I 3'f1is'} swarm d I 3 S t0- fit snuglyab'out the-cylindrical positio'n' mg wal1 53} thereby f to locat th'e -oti-ter wall I3 of ft'iie speaker in -an= accurateand con'ce ritri reflation with respect to the otherpart or the; s eaker. Undesired'i stressonthawa'ir of the-'5 diaphragm is" avoided by making the shouider fl of a. :h'ei-ght considerably greater than tlie thick mess-of the diaphragm flange 55-; andhence*-t1i'e fiange tfl 0f the--wallf--l 3 5s in effect:

a lateral sense with the shoulde1f55an magi-ap ply stress to the: cylindrical wall; fi-i i-"of the-o-iaphra-gm merely in compr'essiona 3 Wjith the structure as thus described it will be" evident that the space between thdiaphragm- I l and the innerpolepiece 2 zicori-stitntes thee soundgchamber 58 =-of the present speake while i the space between thedi apliragrn andi tlie outer end{ of thewalll 3-f constitutes {aback cliamb erf-59r Tl ie'bacli chamber :59 may 'beQvr-lt d'fbyyelets Ii-Df Wh-ich are extended throi i-g'h the Walt-=13 at diametrically opposite. points; and these? eyelets lifl serve as =terminals to whiofr the ends or leads of -theavoice coil may be connected;- Thns the ends-of the wires which fomrthe -voice coi-l are extended 5 along opposite sides of the mite face ofthe-cylindrica1 forml49 to tlie 1::ortior r-=54' of the -diaphragm and' are -led opposi'tadirections along-the portion 51- to; diame'tri'callyopposite 4-5 points adjacent the-1 annularportion ca etthe V diaphragm; atwhich-points=the ends of' the-wires1 are extended through: the diaphragm and iarei ledradially inwardly along -th e port-ton il and are connected to the respectiveeyelets 6Il as by solder 501% ing; Forclarity 'ofidisclosure the endsmtithe wires' ara in: some instances Show being spaced irom the cylindrzioal coil' sapport 49: and. trom'the' face of the: portion it of-the diaphragm; but in practice-theses w-ii 'es are secured toth'e- 55. surface'by adhesiver O'n the surfabe of the por tion 51: of i the. diaphragm; whichtis :adj acent' to the eyeletsi: 60, the ends o-fl the wires may-rbe free ofthe diaphragmpcrtiona 5t}; thereby to permit free movement of the diaphragmr The. space which-is-included betweerr the annular pole" piece-2 I :and: the ortion S mon the diaphragmris also:vented or placed'rin-free communioatiomwitm the-' back: chamber-'5 9 by a=plurality of openings-62.1 formed in the annular portion 5| oft the =dia= 85f phrag mg It is toube understdod in this connection that in: some instances the eyelets t; 60? may": be closed by means such -as a plastiersealing com I poiindg forcby so doingthe frequency respcmseofsv the diaphragm may The modifieob on damped to meetrthe demands of-sometypesof worka Theaspeaker: I I] :fWhiChIiSithllS! providedirnaysbe mounted uponza: headband' I I -or.. other suitable: supperttimdifferenti ways, but; as showmimFigsa 21'anda3-rsuch: a; mounting; is; attained: through:

?; the mounting .of aznutza-fifiiwithin :thzm'zallji I scand centrally thereof. The nut 65- is accessible through a bore or passage 66 in the wall 1.3, and

on opposite sides of the bore 66 a pair or ribs 6'! are moulded or otherwise formed upon the outer side of the wall. The head band H is formed from a relatively flexible strip 68 of a metal such as steel, and the strip 68 is of such a width that it may'flt snugly between the two ribs 61. The strip 68 has a plurality of openings 69 formed therein at longitudinally spaced points, and a screw may be inserted into a selected one of the openings 69 and may be threaded into the nut 65 to hold the speaker I6 and the head band H in an assembled relation. The head band H as shown in Fig. 1 includes an insulated covering H extending relatively close to the ends of the strip 68, and the connecting leads or wires 12 are moulded into the covering H along the opposite side edges of the strip 68. The extending ends of the wires 12 are connected as by soldering to the respective eyelets 60 and an electrical circuit is thereby established from the leads 12 to the voice coil of the speaker. The wire 12 may be extended from the covering H of the headband at any desired point as, for example, centrally of the headband as indicated at 14.

The portion of the diaphragm M which is located radially inwardly of the cylindrical wall 50 constitutes the active portion of the diaphragm, and this portion of the diaphragm is shaped to provide a slightly dome-like form, and the inner face of the wall [3 is extended to provide a similar dome-like form to provide a back chamber of substantially uniform depth and thereby attain a uniform loading of the rear face of the diaphragm. The other or active face of the diaphragm I4 is also arranged to be substantially uniform loaded during operation of the diaphragm, and this end is attained through the formation of a. sloping annular surface 1'6 on the adjacent face of the pole piece 22. The slope of the annular surface 16 is preferably such that the sound chamber 58 has its smallest longitudinal dimension at the radially outer edge of the sound chamber. Thus the spacing between the diaphragm l4 and the surface 16 gradually increases toward the axis of the speaker.

In the speaker which is thus provided, the vibration of the diaphragm id in response to variations in the intensity of the voice current impressed on the voice coil results in the creation of sound waves within the sound chamber 58, and such sound waves are eifectively transmitted to the loading cavity of the speaker and hence to the ear of the user. The mounting and arrangement of the diaphragm [4 are such that the diaphragm has a high fidelity of response over a wide range of frequencies, and hence thepresent speaker, even in an exceptionally small size in which the diameter is somewhat less than one inch, has been found to be effective to re-- produce speech and other sounds with greater intelligibility than prior speakers of a. corresponding size.

The structure illustrated in Figs. 1 to 5 of the drawing whereby the present invention attains the desired accurate location of the voice coil structure in the annular magnetic gap may be varied different respects, as for example, in the manner illustrated in Fig. 6 of the drawing which illustrates an alternative form of the invention. In this form the invention is embodied in a speaker'lfl' wherein the major elements areof the same general form and are disposed in a generally similar relationship as in the form of 8,. the invention disclosed in specific description as to such parts and relation ships will be confined mainly to those aspects where difierences of form or relation are found. The speaker H] has a housing l2c closed at its larger or outer end by a disk-like wall l3? which is. held in place by an inwardly turned flange 42. The housing l2c has a cylindrical portion similar to the portion I2' and this cylindrical portion merges directly with the inwardly curved portion 43 rather than through a shoulder such as the shoulder 41. Thus in this form of the invention the resilient grommet 45' which is inserted in the end opening-44' is relied upon to act between the and the .outer wall l3 in firmly clamped relation to each other endwise of the speaker and against the end flange 42; 1 r

The diaphragm I4 has a flat annular portion 51 disposed between the edge surface of the flange 46' and the opposed flat annular surface of the pole piece 2| so as to be clamped therebetween. Accurate location-of the diaphragm is assured through the provision of a cylindrical locating wall section 53 formed in the diaphragm 14' about the outer edge of the flat portion 5| in such a position and relation as to embrace a cylindrical locating surface 55' afforded by the radially facing surface, of a rabbeted groove formed in an annular corner of the pole piece 2 i A flange 53" preferably extends from the cylindrical locating wall section 53 to impart stiffness to the wall section 53.

Another cylindrical locating wall section 50' is also formed in the diaphragm M to enable accurate mounting of the cylindrical .coil supporting form-49' on the diaphragm, and in this instance the'wall section 58'.extends fromthe annular portion 5| away from the magnetic gap 30', and the diameter of the wall section 50' is such that the coil supporting form 49' may extend snugly within the wall section 56'; and the parts are securedin position by adhesive or other suitable means. Inthe assembly of the parts, the location of the, coil supporting form 49' within the wall section 50 with the-end of the form 49* engaged with the portion 'ofthe diaphragm radially inwardly of the wall section 56" insures that the voice coil structure 3! is concentric with the axis of the diaphragm l4, and hence in the assembled speaker the voice coil structure is located accurately in the annular magnetic ap'30.'- Y I The pole pieces 2| and 22 are held in properly spaced relation by a nonmagnetic spacing ring 24'; and the magnet 15 and the pole pieces are held together We; central or axial eyelet 32 in substantially the same. manner as in the other embodiment of the invention, but as shown in Fig. 6, the sound chamber 58' is defined onone side-thereof by an. annular baflie plate 16'. fixed concentrically on the pole piece 22" and affording a sloping; surface-similar to the surface "and borderingthe flanged end fof-the eyelet 32'.

The t-backchamb'er 59, may bevented if desired by metal eyelets 60' extending through the outer or mounting plate l3", andthe ends of the wires from thevoice' ,coil' are led through the portion 5| iof the'diaphragm l4 and are connected to therespective eyelets 60-in a manner similar to'that employed in the structure of Figs. 1 to5j. Vent openings 62':in the portion 5| of the diaphragm 14' connect thespaceadjacent Figs. 1 to 5, and hence to voice orsignal currents'impressed on the voice coil.

The speaker is. arranged for association with a headband I! havingprojecting conductors '80 which extend slidably through spaced parallel bores 8| formed in a boss 83jmolded on and as a part of the wall l3. Thusthe recesses 84 open into the back chamber 59', and angular contact brackets 85 are disposed in suitable rooves in the inside face of the wall, 13' so that one arm of each bracket 85 is heldin place by one of the eyelets 50' Whilethe other arm of each bracket 85 extendsinto the adjacent one of the recesses and engages the side of the conductors 80; Thus the' contact brackets 85 are electrically connected to opposite ends of the voice coil, and the arrangement is such thatwhen the conductors 80 are projected through the bores 8|, an effective frictional engagement of the conductors 86] with their respective contact brackets 85' establishes the desired electrical circuit to the voice coil; The frictionaleng-agementof the contact brackets 85 with the conductors 80 "is such that the speaker I5 may-be adjusted on the headband I l merely by movement of the speaker along the conductors 80'.

In the embodiment of the invention shown in Figs. 7 to 9; inclusive; the-presentinvention is embodied in a speaker- Illa which is adapted for more convenientmountingupon a headset band I la of a headset, and'in addition, this embodiment'of the invention includesa diaphragm and voicecoil assemblywhereby accurate assembly of the parts of the speaker is facilitated. The embodiment of theinvention disclosed in Figs. 7 to 9 includesa' magnetic circuit wherein the elements are form-ed and related in substantially thesame manner as in the previously described embodiments of the invention, therebeing an inner pole piece 22a, and an outerpolepiece '2 la-separated by a spacing-ring 24m and the two pole pieces are heldin an operative relation with respect to apermanent'magnet 1511 by a tubular member 32a which forms aloadi-ng chamber in the same-generalmanner-as the member 32 disclosed in the embodiment of the invention shown in Fig. 3. i The tubular member 32a, however, is permanently associated with one element lZa of asection'al housing; the element I2a of the housingsb'eing molded from a moldable insulating material-such as acellulose plastic, and the tubular member'32ais molded in the endwall of the casin'g section I 2a with an interlocking means such as spaced'flanges 9U engaged with the material o'fithe casing section I 2a; 5

The other'section l3a ofth'e'casing: includes a wall portio'ngenerally similar to the wall It of the other embodiments =ofztheinvention; and a flange: 9 'is .moldei1 about the edge of 'this wall to providescrew-threads as at '92- to engagecomplemental screw threads: formed on outer pieriphery of theop'en en'd'of thecasing-section [2a. The casing section I3a hasan'annular shoulder 40a formedinteriorly of'theflange92 to" engage anannular clamping portion 54m-of' a diaphragm structure Ma to clamp the 1 diaphragm struc ture' against the outer pole piece 21a: This clamping action is'attained when the twosect-ions of the casing are screwed." together, it being noted that clearance isprovided at 93 'between the pole piece Zla'an'd' the end 0f the casingbsection l2a, thereby" to 1 insure proper clamping iof the diaphragm betweeir the shouldermw and the outer pole. piece andproper clamping of the pole pieces against the magnet I 5a;

In this embodimentfof theinventionthe diaphragm andvoiCecoil structure iformed' in a novel manner which facilitates theattainment of the desired; accuracy of'relationship'between the operative elements of, the' transducer; To this end the diaphragm and voice coil assemblv isconstructed in twoseparatly formed parts whichare so formediand related; thatthley may' be' readily placed in the-'desiredaccurate relation-- ship with respectto each other. To this end the mounting portion 546:; the-flexingportion 5 m and the cylindrical voice coil support-19d are moulded as an integral unit which is completed by mounting ofaloading pprtion thereon inaa'closing relationto' one endf' rthe'voice coil support 49a; The arrangement isc'such that the clam-ping portio 54a, merges with a sl iortjcylindricallocat ing wall portion 553% which in a the assembled speaker is located in'a snuglysurroun-dingrelationship with respect 'toan annular shoulder- 55w formed on the outerpole'piece21a; Thaw-all section 53 merges with} an "an'g'fularly disposed portion 52a which is in turn-j connected to the flexing portion m of "the diaphragm, an'datjits inner peripheral edge of thefixingportion 5la' is joined integrally to one end of the cylindrical voice eon support 49d, Thus 'it will'be 'clearthat the voice coil support 49d and" the locating wall' 53d. may be molded orbotherwise formecl' so' as to be concentric to each other, and th rough tIie formation of, the shoulder 555'on'the'outer pole piece Zla in anjaccurate; concentric relationship with respect to the annular magnetic gap-30a; the desired interrelationship of the operative parts of the speaker may bj'attaind in 'every instance" as i an incident tothe assembly" or 'these parts. I

In the formation; oithe; cylindrical vo ce coil support 49a, the 'materialthereof is iniolded to provide'an annularshoulder S B' 'Wh'ich acts as a guide forlqcating the voie 0011 on thevdice coil support, and thus,- since the voicecoil supportis molded in a predetermined relation to the flexing portion {ila and the mounting portion 54cl' of the diaphragm, this construction insures that' jthe voice coil will :be normally located ifr the desired relation to the magnetic With th voice'coil' supportjad' formed inte grally with the iiexin-gportionilaof the-diaphragm the loading area or'central [section95 of the dia a m y "be re dily andv asily 1 cated in the desired relation to theivoice coil-{and this end is prererabiy attained, through'theformation of a cylindricalwall'section 91 at; the other edge of'thelloading section 9550 that the cylindrical sectional maybewt l pp d s u ly within the voice coil 'supp'ortlfla', Unliormity of l t ns p m he assure by he for a o of an outwardly projecting flange 98atthe 'end of the cylindrical wall 91, in'the assembly of the parts-the loadingsectionfi is'icrc'zegl inwardly into the voice coil support 49izuntilthe flangefifi n a e the fl x po t onfi It or the di phra and; the parts are sec ed"inthlsirela ionby means such as adhesive. 7

The 1eads orwires fromthe opposite ends bf the voice coil are extended along the outersur; facebr the voice coil s ort 49a tQWQrdwthe fiexing section 61a of the, diaphragm and are then extended 1 outwardlyr andlthrougli the flex ingsection 510, adjacent to the outer edgethereof so "thatlthe leads may, be connected to" suit ble t rminal means. 7 In the embodiment gen e n;

V 11 vention shown in Figs. 7 to 9 these terminal means are constructed and arranged for cooperation with a novel mounting and connecting devicewhereby the speaker Ia may be quickly and easily associated with the connecting device so as to establish the desired electrical circuit to the-two ends of thevoice coil. The connecting device asherein shown is in the form of a headband I Ia which has the two conductors included therein. Thus the headband IIa comprises a central insulating strip I00 against one side of which a conductor strip IOI made from a material such as silver is positioned. A resilient strip I02 made from a material such as Phosphor bronie is positioned on the other face of the conductor strip IN. A second flexible strip I03 made from a material such as Phosphor bronze is disposed on the other face of the insulating strip I00 while a second conductor member I04 made from a material such as silver is disposed on the otherface of the resilient strip I03. The several strips which are thus used to form the headband Ila are held together by a plurality of rivets I05 which extend therethrough and are insulated therefrom by insulating sleeves and Washers I06 and I01 respectively.

The terminal means employed in this embodimentof the invention are arranged to be quickly and easilyassociated with the headband Ila, and to this end the terminals H0 and III are in the form of headed studs which extend through the end wall of the casing I 3a and are riveted in position as shown in Fig. 9. The headed studs I I0 and I I I are preferably tubular in form so that the leads fromthe voice coil may be extended therethrough and may be soldered thereto at the exposed outer ends thereof asindicated at 212.

The terminal H0 is formed with spaced annular flanges I I2 and H3 thereon, the spacing of these flanges being substantially equal to combined thickness of the'resilient strip I03v and the conductor strip I04, and these two strips are formed with aligned keyhole slots II4 therein so that the flange II2 may be passed through the large end of the keyhole slot II 4 and into an enlarged clearance opening 5 which is formed in the strips I00, IN and I02. After this has been done the head band I la may be moved endwise so as to engage that portion of the stud 01' terminal IIO'which:1ies between the flanges H2 and H3 with the-narrow portion of the key hole slot II4. Thus. the headband is secured to the terminal H0 against separating'movement away from. the speaker I0a, and as'an incident to the establishment of thisrelation, the conductor strip I04 is engaged with and electrically connected to the flange I I3 of the terminal II 0.

A generally similar connection may also be established between the terminal II I and the other conductor strip .IOI of the headband, and in accomplishing this result the terminal II I is mounted on an outwardly projecting boss IIB formed on the casing section I3a. Thus the flanges H2 and N3 of the terminal III are disposed in different planes than the corresponding flanges on the terminal H0, and are adapted for operative association with a keyhole slot I I1 formed in the resilient strip I02 and the connector strip IOI. A clearance slot H8 is formed in the strips I00, I 03 and I04 opposite the keyhole slot 1, this clearance slot being arranged to receive the boss I I6 and the flange I I3. The spacing of the flanges I I2 and I I3 is such that after the flange .I I3 ofthe terminal III has been inserted through the large end of the keyhole slot 5 flanges.

12 I II, the headband I la maybe shifted in an endwise direction to engage the narrow, portion of the keyhole slot I IT with that portion of the terminal III which is located between the two This establishes an electrical connection between the strip IM and the terminal III, and in addition, the flange II2' holds the headband I Ia against movement away from the speaker I0a. To hold the headband IIa. against endwise movement, thereby to maintain the small ends of the keyhole slots in engagement with the terminals, a releasable latching means is provided which acts between the headband and the speaker I011. The latching. means as herein 15 shown is afforded by a rounded boss I formed on the end wall of the casing section I3a intermediate the terniinals I I0 and I I I in position to engage a recess I2I formed in the end of one of the rivets I 05. This engagement is, of course,

20 resilient, due to the material from which the headband Ila is formed, and hence as the headband He is shifted longitudinally to effect the desired engagement of the -keyhole slots with the terminals [I0 and III, the recess I2I snaps into engagement with the boss I20. It will be clear,

therefore, that the headband is effectively con- ,nected with the terminals of the speaker in a simple and effective manner, and that as in incident to this connection, the proper electrical connections are established to the voice coil. The

headset is then ready for use, and if desired, a resilient guard member 45 a. may be associated with the output end of the speaker, this being attained through the provision of a flange I 22 on the tubular member 32a in position to be engaged with a groove I23 formed in the inner periphery of the guard member 45a.

In theembodiment of the invention shown in Fig. 10, the speaker I 01) is adapted to be associated with a headband II b, and in this headband the voice current is transmitted through resilient strips made from Phosphor bronze rather than through separate conductor strips as in the other embodiment of the invention. 7 In the speaker ID!) the magnet I 5b, the inner pole piece 22b, the outer pole piece 2") and the spacing ring 24b are substantially the same as hereinbefore described in connection with the other embodiments of the invention. In this embodiment of the invention, however, the central tubular member 32b is associated with the casing [217 formed from a non-magnetic material such as brass, and this is accomplished by the formation of a flange I25 on the outer end of the tubular member 321).

The opening'at the smaller end of the casing I2b is arranged about a flanged shoulder I26 and the material of the flange I25 is peened over the outer face of the casing I2b to hold thecasing in place on the tubular member 32b. The inner end of 00 the tubular member 32b is flanged at 34b so as to engage the inner face of the inner pole piece 22b, while the flange I 25 engages the flat face 3% of the magnet I5b. Thus the formation of flange 34b on the inner end of the tubular member 321) serves to hold the elements of the magnetic circuit in the desired assembled relation within the casing I212. The outer end of the tubular member 32b is extended beyond the flange I25, and is flanged at I22b to hold a resilient guard member 45b in position to engage the ear of a user.

In this embodiment of the invention the casing section I2b is utilized to hold the mounting wall l3b in position on the outer pole piece 2Ib and the mounting wall I3b has a flange 402) which is adapted, to engage the mounting portion 54b of re the diaphragm Mb. 'I'he diapl-iragm Illb maybe formed as disclosedin l lgs. 1 to 5;- or maybe formed-as illustratedin -F'ig-s.- 8 and ybuttin this embodiment of the invention the mounting flange 54b of the" diaphragm has a slot formed therein through which a-- relatively narrow tongue I28 formed on the flange tub of the wall 1 3b maypass into a-correspondingslot I29 formed in-the outer pole piece 2 lb, thereby to hold the diaphragm I 4b and the'mounting wall Itb against rotative movement relative to each other and relative to the elements of the magnetic circuit. With this construction, the edge of the casing I211 may be easily flanged inwardly as at 42b to hold the'mounting wall I3b securely imposition in the desired clamping-relation to the diaphragm Mb.

In this embodiment of the, inventionsimilar terminals IIIlb and NH) areprovided'uonz: the mounting wall I3b, and, these terminalsw are adapted for association with l the: headband; II b insubstantially the same manner as in: the embodiment shown in Figs. l t-o :91- In thezem'bodiment of the invention shown .in Fig. 10, however, the headband is formed from=a strip ofzinsulating material such as cellulose plastic onzopposite sides of which a pair of resilient strips I021: and 13b are'fixed by means suchgas rivets I'll'5b. Those portions of the rivets! Ital) which might engage with the conductor strip lll2bparejinsulatedrtherefrom by means-such as fibre? eyelets.

or sleeves I 06b. Thus, in thisremb'odimentrof" the invention, the resilient strips I621) and I031), which are made preferably from a material such as Phosphor bronze, are relied upon to serve as conductorsand thespacing, ofzthe flanges: on

terminals Iltb and III!) is so arranged that the desired electrical connection is established between the conductor strips and their respective terminals when the keyhole slots 4b and Ill?) in the headband I lb are engaged with the respective terminals HM) and lb. Such engagement is maintained by the resilient latching action of a recess I2Ib formed in one of the rivets IOEb and engaged with a rounded boss IZIIb formed on the mounting wall Mb.

vIn the embodiment of the invention shown in Fig. 11, the two terminal studs IIOc are of the same form as the stud II!) and are mounted with the corresponding flanges thereof in the same plane. In other Words, theboss II 5 is eliminated in this form of the invention, thereby to reduce the thickness of the speaker as a whole. With this arrangement the two conductors which are to be connected to the respective terminals I IIlc are disposed in the same plane and are provided by two semi-circular metal plates H120 and IU3c having connecting arms I extending therefrom so that lead wires may be soldered to the arms Isl The two plates H320 and I030 are mounted on or recessed into one face of a circular plate I3I of insulating material so that the straight edges of the two plates are spaced slightly from each other, and the plates are secured in such positions by rivets W50 similar to the rivets IE5. The plates I920 and. Ill3c have keyhole slots H and H10, respectively, formed therein at diametrically opposite points in such a relation that the heads of the two terminal studs IIilc may be inserted through the large ends of the two keyhole slots. The small ends or extensions of the slots are extended in 0pposite directions and are concentrically related so that the speaker may then be rotated about its axis to engage the reduced portions of the studs IIIlc with the narrow portions of the slots 14 Illlcand. I I la. In such movementf. the headsxof the studsspass into clearance" openings; H50. and I I8c formed in the insulating plate I3I, and the two studs are electrically connected to the'studs I920. and: lilac-as in the. embodiments ofthe'inventionshowniniFigs. 7 to 10. This: engagement of the parts. isvmaint'ainedby latching engages ment'of: the: recessed end ofv one ofthe." rivets I050 with a boss-suchlas the-boss- IZOD-applie priately positioned on the. outer wall: of the speaker. lnsthisform' of theinvention thesplate l 3! may bezmountedion aheadband, ormaysserye merely as "a: connecting means-:for: connecting-the lead wiresuto the' voiceccoil. In this-latteriinstance; amolded'zeawpieceroffconventional design is fastened on' the flangedtend I22'or 'I25wofrtlie speaker so. that th'eear-pie-cex may-be inserted user: to; act

ducers: of. the: dynamic: typeto beproduced in such .a." manner'as to insure fidelity" of perform:- ance and; accuracy. ofv response; overra wideqrange of; frequencies: The relationship of i theparts is such that transducers may beproduced: over a wide range of sizes;%sincluding exceedingly small sizes, and in all instancesthe mereassemblyof the component partscof "the transducer-results .in the desired accuracy of: relationship; of l these parts, and: hence; the desired i excellence of perfcrman-ce is invariably; attained; wherethepres ent invention .isxembodiedtin-a speaker 'it willub'e evident that the particular arrangement of; the elements "of: the magnetic circuit is such" thatsall space within the speaker casing is efliciently utilized, and as a result exceptionally good performance characteristics may be embodied in a relatively small speaker. The novel form of permanent magnet which is provided by the present invention contributes in a great measure to the simplicity and efiiciency of the transducer, whether such transducer be embodied as a speaker or as a microphone, and moreover, this novel form of permanent magnet enables the other elements of the magnetic circuit to be accurately related to the magnet and to each other in such a manner as to produce accuracy of size and form in the magnetic gap.

It will also be evident that the present invention, through the provision of a novel diaphragm, has simplified the manner of assembly of dyna mic transducers, and this simplification. is attained in such a way that the elements of the transducer when assembled are invariably located in the desired relationship to each other. Moreover, the formation of the voice coil support integrally with the mounting flange'of the diaphragm contributes in a substantial degree to the attainment of the desired location of the voice coil with relation to the magnetic gap, and through the formation of a guiding shoulder on the voice coil support, the manufacture of this portion of the transducer is materially simplified. The present invention also enables speakers to be embodied as parts of a headset in an exceptionally simple manner such that the desired electrical connections are established as an incident to the mounting of the speakers upon the headband.

Hence, While I have illustrated and described preferred embodiments of my invention, it is to be understood that these are capable of variation and modification and I therefore do not wish to be limited to the precise details set forth, but

desire to avail myself of such changes and alterations as fall within the purview of the following claims:

I claim: 7

1. In a speaker adapted for use in a headset, means forming a magnetic circuit including inner and outer annular pole pieces concentrically located and spaced to provide an annular magnetic gap therebetween, a diaphragm mounted on said outer pole piece and having a voice coil structure carried thereon and extending into said annular magnetic gap, said diaphragm being spaced from one face of said inner pole piece to define a sound chamber, means defining a back chamber on the side of said diaphragm opposite from said sound chamber, a permanent magnet forming part of said magnetic circuit and comprising a centrally bored hub having one end engaging said inner pole piece and having an annular skirt extending outwardly from the other end of the hub and then in an endwise direction in spaced relation to said hub and into contact with said outer pole piece, and a, tubular fastening member extending through the bore of said hub and operatively engaged with said magnet and said inner pole piece to hold the same together,

said tubular fastening member openin into said ing portion and an integral flexing portion extending inwardly therefrom, said sheet of material also being formed to provide a central load- Y 16 ing portion offset from said flexing portion and having a relatively short cylindrical wall'portion joining said loading portion and said flexingportion, and said mounting portion and said flexing portion being joined by an integral and relatively short cylindrical wall section located concentrically with respect to the cylindrical wall section which joins said flexing portion and said loading portion.

WEBSTER E. GILMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,375,707 King Apr. 26, 1921 1,568,721 Buther et a1. Jan. 5, 1926 is 1,747,778 Kuchenmeister Feb. 18, 1930' 1,809,911 Pridham June 16, 1931 1,843,367 Langley Feb. 2, 1932 1,875,004 Horsburgh Aug, 30, 1932 1,899,561 Dorsey Feb. 28, 1933 1,907,723 Bostwick May 9, 1933 1,923,965 Breman Aug. 22, 1933 1,941,776 Abrahams Jan. 2, 1934 2,037,187 Wente Apr. 14, 1936 2,058,555 Betts et a1 Oct. 27, 1936 2,105,934 Stevens Jan; 18,1938 2,107,757 Kinsley Feb. 8, 1938 FOREIGN PATENTS Number Country Date 399,556 Great Britain Oct. 9, 1933 

